A dual mode moisture and
pressure sensor for monitoring
critical systems
John Dyer
MEMS Sensor
Analog
Front End
The Analog front end comprises of 3 sections:
• Wheatstone Bridge
• Instrumentation Amplifier
• Analog To Digital Converter
There are two sets of Wheatstone bridges and
two sets of instrumentation amplifiers to sense
the two pairs of piezo-resistors on the sensor.
Instrumentation Amplifier
• Each instrumentation amplifier
comprises of three operational
amplifiers
• Discrete operational amplifiers
were used to construct this
configuration
• The ability to set bias voltage is
a critical feature
• Cannot detect differences below
or above the rail voltage
Analog To Digital Converter
Digital
Processing
Section
The STM32 microcontroller
was chosen to handle all the
processes after signal is
digitized
• Communications with the
ADC and wireless
transceiver
Different STM32 MCU’s can
perform faster and include
more memory while being
cross-compatible
• Failure detection
algorithm
It handles the following
processes:
• Health monitoring
algorithms
• Temperature monitoring
The STM32 can be
programmed on its own
software with a serial wire
debug connection
Communications
Structures
• Several communications layouts are possible
and are discussed including:
• Hard-Wired Systems
• Low Power Transceiver setup
• Dedicated board used in handling
communications
• Minimal power consumption option
PCB
Prototype
Design
Enclosure Options